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<TITLE> Virtual Prototyping of Mechanical Assemblies </TITLE>
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Virtual Prototyping of Mechanical Assemblies
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<p>

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  <!WA0><img src= "http://www.cs.utah.edu/projects/robot/IMAGES/vp-slave-mesh-180H.gif">
  <!WA1><img src= "http://www.cs.utah.edu/projects/robot/IMAGES/arches.gif">
  <!WA2><img src= "http://www.cs.utah.edu/projects/robot/IMAGES/sda-master-tom.gif">
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<P>

Current generation CAD systems provide little support for prototyping
mechanical assemblies.  We are
creating an integrated design and simulation system to address this
problem.  Fundamental to the effort is the investigation of effective
mechanisms for allowing a designer to interact with an assembly of
parts in a ``virtual'' manner, prior to creation of any physical
prototypes.  The designer will be able to touch, hold, and move models
of parts and assemblies as well as see them in rendered views.  The
result will be an environment in which part interactions can be
considered in a more natural manner than is possible with current
technology.  Part interactions and articulations of high DOF assemblies
can be considered early in the design process.  Assembly procedures can
be evaluated at the time when parts are designed, without the need to
explicitly specify assembly sequences or constraints.  Even greater
advantages will accrue in the design of devices intended for human use,
since manipulability can be examined without the need to fabricate a
physical prototype.  Finally, the virtual display tools that are
integral to this project will give designers a better appreciation for
complex part geometry than can be gained from traditional CAD displays,
which have only limited 3-D information. </p>

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<H3> Faculty </H3>
<UL>
  <li> <!WA4><a href = "http://www.cs.utah.edu/~jmh"> John M. Hollerbach</a>, PI
  <li> <!WA5><a href = "http://www.cs.utah.edu/~cohen">  Elaine Cohen</a>
  <li> <!WA6><a href = "http://www.sarcos.com/Jacobsen.html">Stephen C. Jacobsen</a>
  <li> <!WA7><a href = "http://www.cs.utah.edu/~thompson"> William B. Thompson</a>
</UL>
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<H3> Staff </H3>
<UL>
  <li> <!WA8><a href = "http://www.cs.utah.edu/~fish"> Russ Fish</a>
</UL>
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<H3> Graduate Students</H3>
<UL>
  <li> <!WA9><a href = "http://www.cs.utah.edu/~freier"> Rodney Freier</a>
  <li> <!WA10><a href = "http://www.cs.utah.edu/~dejohnso"> David Johnson </a>
  <li> <!WA11><a href = "http://www.cs.utah.edu/~nahvi"> Ali Nahvi</a>
  <li> <!WA12><a href = "http://www.cs.utah.edu/~dnelson"> Donald Nelson</a>
  <li> <!WA13><a href = "http://www.cs.utah.edu/~tthompso"> Thomas Thompson</a>
</UL>
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<p>

CAD systems for all but the simplest of mechanical parts must be able
to provide the designer with a clear sense of three-dimensional object
geometry.  Usually this is done with standard graphical rendering
techniques involving perspective, shading, and simple animation.  When
such tools are used for assemblies of parts, we often hear designers
complain:  ``What I really want to do is get my hands on the parts and
see how they fit together.''  In fact what is happening is that the
conventional display technologies are not providing the user with
sufficient information about the geometry and manipulability of the
objects in question.

<P>

A key aspect of addressing this limitation is to augment visual
rendering of geometric models with haptic interfaces which allow direct
manipulation of modeled objects.  Such interfaces must include accurate
anthropomorphic geometry and provide realistic force feedback if they
are to be of real value.  The Sarcos Dextrous Arm Master represents
arguably the most advanced force-reflecting exoskeleton available
today.  The upper seven degree-of-freedom arm component matches the
redundancy of the human arm, while three degrees of freedom are
provided to the hand; in total, there are 10 degrees of freedom and of
force reflection per master arm.  In the hand, there is a two
degree-of-freedom thumb, a fixed forefinger, and a one
degree-of-freedom flexing index/middle finger.  The Sarcos Dextrous Arm
is based on hydraulic actuation, which is unmatched for torque density
and bandwidth for this application.  The result is a master that is
much more compact and of higher performance than would be possible with
electric motor drives.

<P>

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  <!WA15><img src= "http://www.cs.utah.edu/projects/robot/IMAGES/real-engine.gif">
  <!WA16><img src= "http://www.cs.utah.edu/projects/robot/IMAGES/gear-chain-2.gif">
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<P>

The pictures above shows a one third scale model for a novel diesel
engine with one cylinder, two pistons, and four crankshafts and
represents of the kinds of assemblies that we are working towards
accommodating in a virtual prototyping system.  The engine involves
complex and interrelated part motions that should be well understood by
designers prior to committing to expensive fabrication operations.  A
full-function virtual prototyping system will let the designer
manipulate individual parts to see how the entire assembly moves.
Virtual prototyping furthermore would allow a designer to consider
possible assembly sequences, modifying parts as necessary to ease the
assembly process.  Finally, a virtual prototyping system with a
sufficiently complete model of the human body could be used to validate
assembly operations for the engine.

<P>

Creating a user interface for virtual prototyping systems
involves solving three largely independent problems: 

<UL>
<li><EM>Visual rendering</EM>
involves creating realistic views of a configuration of parts.

<li>There are two aspects to <EM>haptic rendering</EM>.  The first
involves giving the user a realistic sensation that he or she is
actually touching and manipulating physical objects.  The second takes
motions made by a user and modifies the models specifying the virtual
world appropriately. 

<li><EM>Contact and interference</EM> computations are
needed to determine part-to-part and user-to-part interactions in the
virtual world.  Visual rendering, haptic rendering, and contact and
interference detection must all exploit knowledge about the nature of
mechanical assemblies, since general solutions are not likely to be
viable.
</UL>

Geometric modeling systems able to support virtual prototyping of
mechanical assemblies need capabilities beyond those of the typical
CAD/CAM system.  Not only must it be possible to design and render
individual parts, but part interactions involving contact, forces, and
torques must be computable in real-time.  When a designer reaches out
to ``grab'' a (virtual) part, the system needs to know when contact
with the part has been made so that appropriate feedback can be
generated.  Once a solid grip has been established, user feedback must
reflect object inertial and gravity forces and assembly forces due to
contact.  For those assemblies capable of articulation, a manipulation
of one part of the assembly must both cause the appropriate motions in
other parts of the assembly and reflect appropriate sensations to the
user.

<P>

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  <!WA17><img src= "http://www.cs.utah.edu/projects/robot/IMAGES/haptic-requirements.gif">
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Standard CAD systems are unable to supply much of the information
needed to support either assembly operations themselves or the haptic
rendering required in a virtual prototyping system.

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